Esterfication catalyst, polyester process and polyester article

ABSTRACT

A catalyst composition for producing polyesters comprises: a) an organometallic compound obtained by reacting an orthoester or condensed orthoester of titanium, zirconium or aluminum, an alcohol containing at least two hydroxyl groups, a 2-hydroxy carboxylic acid and a base; and b) at least one compound comprising germanium, antimony or tin. Polyesters obtained by esterification reaction in the presence of the catalyst compositions according to the present invention exhibit improved melt properties and are particularly suitable for production of textile and commercial fibers, films and rigid packaging.

BACKGROUND OF THE INVENTION

[0001] The invention concerns a polyester fibre composition and aprocess for its manufacture which utilises a novel organotitanium ororganozirconium catalyst

[0002] Antimony (Sb), tetraisopropyl titanate, and triethanolaminetitanate are known catalysts for esterification processes. Also,organotitanium compounds and, in particular, titanium alkoxides ororthoesters are known as catalysts for esterification processes. Manyorganotitanium compounds which are effective catalysts in themanufacture of polyesters such as polyethylene terephthalate are knownto produce unacceptable yellowing in the final polymer. U.S. Pat. No.5,866,710 describes an esterification process using a catalyst systemwhich comprises the reaction product of an orthoester or condensedorthoester of titanium or zirconium, an alcohol containing at least twohydroxyl groups, a 2-hydroxy carboxylic acid and a base. The polyestersproduced by such a process show a reduced amount of haze and yellowingin comparison to a known titanium isopropoxide catalyst U.S. Pat. No.5,866,710 teaches that the resulting polyesters are useful in films andbottles; the reference does not teach or suggest using the resultingpolyesters in fiber or yarn.

[0003] When polyester articles are formed from molten polyester, whenprocessing polyesters into textile fibres or bottles for example, thepolymer is melted and may be held in the molten state for a period oftime before being shaped by e.g. spinning or injection moulding. Two keyrheology measurements: shear viscosity or complex viscosity as afunction of shear rate or frequency and extensional viscosity as afunction of shear stress are used to characterize polyesters. Zero-shearviscosity is typically taken as an indication of polymer molecularweight while the transient extensional viscosity is an indicator of thepolymer's extensional response to stretching.

[0004] We have now found a catalyst composition for producing polyestersin particular which exhibit unexpectedly improved melt rheologicalproperties compared with polyester of the same intrinsic viscosity madeusing known catalyst systems, and which are therefore particularlysuitable for making polyesters for such applications.

SUMMARY OF THE INVENTION

[0005] It is an object of the present invention to provide an improvedprocess for preparing polyesters and an improved organometalliccomposition for use as a catalyst in such processes. It is also anobject of the present invention to provide an improved polyester formelt processing applications and also formed articles made from theimproved polyester.

[0006] According to the invention we provide a catalyst compositionsuitable for use as a catalyst for the preparation of an estercomprising:

[0007] (a) an organometallic compound which is the reaction product ofan orthoester or condensed orthoester of titanium, zirconium oraluminium, an alcohol containing at least two hydroxyl groups, a2-hydroxy carboxylic acid and a base, and

[0008] (b) at least one compound of germanium, antimony or tin.

[0009] According to a second aspect of the invention, we provide aprocess for the preparation of a polyester which comprises carrying outa polyesterification reaction in the presence of a catalyst, whichcatalyst comprises (a) an organometallic compound which is the reactionproduct of an orthoester or condensed orthoester of titanium, zirconiumor aluminium, an alcohol containing at least two hydroxyl groups, a2-hydroxy carboxylic acid and a base, and (b) at least one compound ofgermanium, antimony or tin.

[0010] According to a third aspect of the invention, we provide apolyester article made by a process which comprises carrying out apolyesterification reaction in the presence of a catalyst, whichcatalyst comprises:

[0011] (a) an organometallic compound which is the reaction product ofan orthoester or condensed orthoester of titanium, zirconium oraluminium, an alcohol containing at least two hydroxyl groups, a2-hydroxy carboxylic acid and a base, and

[0012] (b) at least one compound of germanium, antimony or tin to form apolyester material having an intrinsic viscosity of at least 0.5 dl/g,as measured by capillary viscometry using the method of ASTM D-4603, andsubsequently forming the polyester article from the polyester materialin the molten phase.

[0013] According to a fourth aspect of the invention, we provide apolyester article containing residues of a catalyst system whichcomprises (a) the reaction product of an orthoester or a condensedorthoester of titanium, zirconium or aluminium, an alcohol containing atleast two hydroxyl groups, a 2-hydroxy carboxylic acid and a base and(b) at least one compound of germanium, antimony or tin.

[0014] The present invention also provides an unexpected result, that isa titanium based catalyst system having improved extensional viscositycompared with prior art tetraisopropyl titanate. This result isparticularly beneficial in making polyester for fiber spinningapplications.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015]FIGS. 1 and 2 show rheological properties for polyester made froma prior art antimony catalyst and a titanium catalyst

[0016]FIGS. 3 and 4 show rheological properties for polyester made fromthe catalysts of the invention and a prior art comparison.

[0017]FIG. 5 shows a measure of crystallinity and orientation index forpolyester fibres of the invention and an antimony comparison.

DETAILED DESCRIPTION OF THE INVENTION

[0018] The organometallic compound suitable for use in an esterificationprocess as component (a) of the aforementioned catalyst compositioncomprises the reaction product of an orthoester or condensed orthoesterof at least one metal selected from titanium, zirconium or aluminium.Normally an orthoester or condensed orthoester of one of the selectedmetals is used but it is within the scope of the invention to use anorthoester or condensed orthoester of more than one of the selectedmetals. For clarity we refer hereinafter to a titanium, zirconium oraluminium orthoester or condensed orthoester, and all such referencesshould be taken to include orthoesters or condensed orthoesters of morethan one metal, e.g. to a mixture of titanium and zirconium orthoesters.

[0019] Preferably, the orthoester has the formula M(OR)₄ or Al(OR)₃where M is titanium or zirconium and R is an alkyl group. Morepreferably R contains 1 to 6 carbon atoms and particularly suitableorthoesters include tetraisopropoxy titanium, tetra-n-butoxy titanium,tetra-n-propoxy zirconium, tetra-n-butoxy zirconium and tri-iso-butoxyaluminium.

[0020] The condensed orthoesters suitable for preparing theorganometallic compounds used in this invention are typically preparedby careful hydrolysis of titanium, zirconium or aluminium orthoesters.Titanium or zirconium condensed orthoesters are frequently representedby the formula

R₁O[M(OR₁)₂O]nR₁

[0021] in which R¹ represents an alkyl group and M represents titaniumor zirconium. Preferably, n is less than 20 and more preferably is lessthan 10. Preferably, R¹ contains 1 to 12 carbon atoms, more preferably,R¹ contains 1 to 6 carbon atoms and useful condensed orthoesters includethe compounds known as polybutyl titan ate, polyisopropyl titanate andpolybutyl zirconate.

[0022] Preferably the alcohol containing at least two hydroxyl groups isa dihydric alcohol and can be a 1,2-diol such as 1,2-ethanediol,1,2-propanediol, a 1,3-diol such as 1,3-propanediol or a dihydricalcohol containing a longer chain such as diethylene glycol or apolyethylene glycol. Preferred dihydric alcohols are 1,2-ethanediol anddiethylene glycol. The organometallic compound can also be prepared froma polyhydric alcohol such as glycerol, trimethylolpropane orpentaerythritol.

[0023] Preferably the organometallic compound is prepared by reacting adihydric alcohol with an orthoester or condensed orthoester in a ratioof from 2 to 12 moles of dihydric alcohol to each mole of the titaniumor zirconium. More preferably the reaction product contains 4 to 8 molesdihydric alcohol per mole of titanium, zirconium or aluminium.

[0024] Preferred 2-hydroxy-carboxylic acids include lactic acid, citricacid, malic acid and tartaric acid. Some suitable acids are supplied ashydrates or as aqueous mixtures. Acids in this form as well as anhydrousacids are suitable for preparing the catalysts used in this invention.The preferred molar ratio of acid to titanium or zirconium in thereaction product is 1 to 4 moles per mole of titanium or zirconium. Morepreferably the organometallic compound contains 1.5 to 3.5 moles of2-hydroxy acid per mole of titanium or zirconium.

[0025] A base is also used in preparing the reaction product which isused as the organometallic compound in the catalyst of the invention.The base may be an inorganic base or an organic base but is generally aninorganic base and suitable bases include sodium hydroxide, potassiumhydroxide, ammonium hydroxide, sodium carbonate, magnesium hydroxide andammonia. Preferred organic bases include quaternary ammonium compoundssuch as tetrabutyl ammonium hydroxide, tetraethylammonium hydroxide,choline hydroxide, (trimethyl (2-hydroxyethyl)ammonium hydroxide) orbenzyltrimethyl ammonium hydroxide, or alkanolamines such asmonoethanolamine, diethanolamine, triethanolamine andtriisopropanolamine. Usually, the amount of base used is in the range0.1 to 12 mole base per mole of metal (titanium, zirconium oraluminium). The preferred amount is in the range 0.1 to 4.0 mole baseper mole of titanium, zirconium or aluminium.

[0026] Frequently, the amount of base used is sufficient to fullyneutralise the 2-hydroxy carboxylic acid but it is not essential thatthe acid is fully neutralised.

[0027] In one preferred embodiment the organometallic compound comprisesthe reaction product of a titanium orthoester, citric acid, a dihydricalcohol and an inorganic base in which the mole ratio oftitanium:acid:dihydric alcohol:base is in the range 1:1.5-3.5:4-10:2-12.

[0028] Typically, the organometallic compound is neutral. It isfrequently convenient to add water together with the base when preparingthe catalysts. Frequently, products which contain water have a pH in therange 6 to 8.

[0029] The organometallic compound can be prepared by mixing thecomponents (orthoester or condensed orthoester, dihydric alcohol,2-hydroxy acid and base) with removal of any by-product, (e.g. isopropylalcohol when the orthoester is tetraisopropoxytitanium), at anyappropriate stage. In one preferred method the orthoester or condensedorthoester and dihydric alcohol are mixed and subsequently, 2-hydroxyacid and then base are added or a pre-neutralised 2-hydroxy acidsolution, is added. In an alternative preferred method the orthoester orcondensed orthoester is reacted with the 2-hydroxy acid and by-productalcohol is removed. Base is then added to this reaction product followedby a dihydric alcohol to produce the reaction product which is used inthe catalyst of the invention. If desired, further by-product alcoholcan then be removed by distillation. U.S. Pat. No. 5,866,710 isincorporated herein by reference.

[0030] Component (a) alone may be used as the catalyst to make polyesterfor fibre applications including textile fiber and industrial fiber. Theterm “industrial fiber” as used herein includes fibre useful in themanufacture of tire cord, broad wovens, seat belts, conveyor belts, Vbelts, air bags, cut resistant articles, and ropes. Industrial fiber maybe made by known methods such as those disclosed in U.S. Pat. Nos.5,085,818; 5,132,067; 5,397,527; 5,630,976; 5,830,811; and 6,071,835;these patents are incorporated herein by reference.

[0031] Component (b) of the catalyst composition of the invention is acompound of germanium, antimony or tin and, in general, any compound canbe used including mixtures of compounds of more than one of thesemetals. The preferred compound of germanium is germanium dioxide.Preferably, the antimony compound is antimony trioxide or a salt ofantimony, for example antimony triacetate. A number of tin compounds aresuitable, including salts, such as tin acetate and organotin compounds,such as dialkyl tin oxides, for example, dibutyl tin oxide, dialkyl tindialkanoates, for example, dibutyl tin dilaurate and alkylstannoicacids, for example butylstannoic acid (C₄H₉SnOOH).

[0032] A wide range of proportions of components (a) and (b) can bepresent in the catalyst composition of the invention. Generally, theweight ratio of component (a) to component (b) is in the range 1:0-1000,calculated as weight of Ti, Zr or Al to weight of Ge, Sb or Sn. The twocomponents, (a) and (b) may be premixed to form the catalyst compositionof this invention before the composition is mixed with the reactants foran esterification reaction. Alternatively, components (a) and (b) can beseparately added to the reactants in order to carry out anesterification reaction according to this invention.

[0033] The esterification reaction of the process of the invention canbe any reaction by which an ester is produced. The reaction may be (i) adirect esterification in which a carboxylic acid or its anhydride and analcohol react to form an ester or (ii) a transesterification(alcoholysis) in which a first alcohol reacts with a first ester toproduce an ester of the first alcohol and a second alcohol produced bycleavage of the first ester or (iii) a transesterification reaction inwhich two esters are reacted to form two different esters by exchange ofalkoxy radicals. Direct esterification or transesterification can beused in the production of polymeric esters and a preferred process ofthe invention comprises a polyesterification process. Many carboxylicacids and anhydrides can be used in direct esterification includingsaturated and unsaturated monocarboxylic acids and anhydrides of suchacids such as stearic acid, isostearic acid, capric acid, caproic acid,palmitic acid, oleic acid, palmitoleic acid, triacontanoic acid, benzoicacid, methyl benzoic acid, salicylic acid and rosin acids such asabietic acid, dicarboxylic acids such as phthalic acid, isophthalicacid, terephthalic acid, sebacic acid, adipic acid, azelaic acid,succinic acid, fumaric acid, maleic acid, naphthalene dicarboxylic acidand pamoic acid and anhydrides of these acids and polycarboxylic acidssuch as trimellitic acid, citric acid, trimesic acid, pyromellitic acidand anhydrides of these acids. Alcohols frequently used for directesterification include aliphatic straight chain and branched monohydricalcohols such as butyl, pentyl, hexyl, octyl and stearyl alcohols,dihydric alcohols such as 1,2-ethanediol, 1,3-propanediol,1,4-butanediol and 1,6 cyclohexane dimethanol and polyhydric alcoholssuch as glycerol and pentaerythritol.

[0034] The esters employed in an alcoholysis reaction are generally thelower homologues such as methyl, ethyl and propyl esters since, duringthe esterification reaction, it is usual to eliminate the displacedalcohol by distillation. These lower homologue esters of the acidssuitable for direct esterification are suitable for use in thetransesterification process according to the invention. Frequently(meth)acrylate esters of longer chain alcohols are produced byalcoholysis of esters such as methyl acrylate, methyl methacrylate,ethyl acrylate and ethyl methacrylate. Typical alcohols used inalcoholysis reactions include butyl, hexyl, n-octyl and 2-ethyl hexylalcohols and substituted alcohols such as dimethylaminoethanol.

[0035] When the esterification reaction is a transesterification betweentwo esters, generally the esters will be selected so as to produce avolatile product ester which can be removed by distillation.

[0036] In direct esterification the acid or anhydride and an excess ofalcohol are typically heated, if necessary in a solvent, in the presenceof the catalyst composition. Water is a by-product of the reaction andthis is removed, as an azeotrope with a boiling mixture of solventand/or alcohol. Generally, the solvent and/or alcohol mixture which iscondensed is at least partially immiscible with water which is thereforeseparated before solvent and/or alcohol are returned to the reactionvessel. When reaction is complete the excess alcohol and, when used,solvent are evaporated. In view of the fact that the catalystcompositions of the invention do not normally form insoluble species, itis not generally necessary to remove them from the reaction mixture, asis frequently necessary with conventional catalysts. A typical directesterification reaction is the preparation of bis(2-ethylhexyl)phthalate which is prepared by mixing phthalic anhydride and 2-ethylhexanol. An initial reaction to form a monoester is fast, but thesubsequent conversion of the monoester to diester is carried out byrefluxing in the presence of the catalyst composition at a temperatureof 180-200° C. until all the water has been removed. Subsequently theexcess alcohol is removed.

[0037] In an alcoholysis reaction, the ester, first alcohol and catalystcomposition are mixed and, generally, the product alcohol (secondalcohol) is removed by distillation, often as an azeotrope with theester. Frequently it is necessary to fractionate the vapour mixtureproduced from the alcoholysis in order to ensure that the second alcoholis separated effectively without significant loss of product ester orfirst alcohol. The conditions under which alcoholysis reactions arecarried out depend principally upon the components of the reaction andgenerally components are heated to the boiling point of the mixtureused.

[0038] A particularly preferred embodiment of the esterification processof the invention is a polyesterification reaction in the presence of thecatalyst composition of the invention. Polyesters can be produced byprocesses involving direct esterification or transesterification. In apolyesterification reaction polybasic acids or esters of polybasic acidsare usually reacted with polyhydric alcohols. Preferred reactants aredicarboxylic acids such as phthalic acid, isophthalic acid, terephthalicacid, sebacic acid, adipic acid, azelaic acid, succinic acid, fumaricacid, maleic acid, naphthalene dicarboxylic acid and pamoic acid andesters and anhydrides of these acids and polycarboxylic acids such astrimellitic acid, citric acid, trimesic acid, pyromellitic acid andesters and anhydrides of these acids. Preferred alcohols includealiphatic straight chain and branched polyhydric alcohols such as1,2-ethanediol (ethylene glycol), 1,4-butanediol (butylene glycol),1,3-propanediol, 1,6-hexanediol, cyclohexane dimethanol,trimethylpropane, glycerol and pentaerythritol.

[0039] Preferred polyesterification reactions according to the inventioninclude the reaction of terephthalic acid or dimethyl terephthalate with1,2-ethanediol (ethylene glycol) to produce polyethylene terephthalateor with 1,4-butanediol (butylene glycol) to produce polybutyleneterephthalate or reaction of naphthalene dicarboxylic acid with1,2-ethanediol to produce polyethylene naphthalenate. Other glycols suchas 1,3-propanediol, 1,6-hexanediol, trimethylpropane and pentaerythritolare also suitable for preparing polyesters.

[0040] The esterification reaction of the invention can be carried outusing any appropriate, known technique for an esterification reaction.

[0041] A typical process for the preparation of polyethyleneterephthalate comprises two stages. In the first stage terephthalic acidor dimethyl terephthalate is reacted with 1,2-ethanediol to form aprepolymer and the by-product water or methanol is removed. Theprepolymer is subsequently heated in a second stage to remove1,2-ethanediol and form a long chain polymer. Either or both thesestages may comprise an esterification process according to thisinvention.

[0042] A typical batch production of polyethylene terephthalate iscarried out by charging terephthalic acid and ethylene glycol to areactor along with catalyst composition, if desired, and heating thecontents to 260-270° C. under a pressure of about 0.3 MPa. Reactioncommences as the acid dissolves at about 230° C. and water is removed.The product is transferred to a second autoclave reactor and catalystcomposition is added, if needed. The reactor is heated to 285-310° C.under an eventual vacuum of 100 Pa to remove ethylene glycol by-product.The molten product ester is discharged from the reactor, cooled andchipped. The chipped polyester may be then subjected to solid statepolymerisation, if appropriate.

[0043] A preferred means of adding the catalyst compositions of thisinvention to a polyesterification reaction is in the form of a slurry inthe glycol being used (e.g. ethylene glycol in the preparation ofpolyethylene terephthalate). Components (a) and (b) can be added to thereaction mixture as separate slurries or mixed to prepare a slurrycontaining both components, which slurry is then added to the reactants.This method of addition is applicable to addition of the catalystcomposition to the polyesterification reaction at the first stage or atthe second stage.

[0044] The amount of catalyst used in the esterification process of theinvention generally depends upon the total metal content (expressed asamount of Ti, Zr or Al plus amount of Ge, Sb or Sn) of the catalystcomposition. Usually the amount is from 0.2 to 1200 parts per million(ppm) of metal based on weight of product ester for direct ortransesterification reactions. Preferably, the amount is from 5 to 500ppm of total metal based on weight of product ester: Inpolyesterification reactions the amount used is generally expressed as aproportion of the weight of product polyester and is usually from 5 to500 ppm expressed as total metal (Ti, Zr or Al plus Ge, Sb or Sn) basedon product polyester.

[0045] Generally, the amount of Ti, Zr or Al used in a directesterification or transesterification will be in the range 0.1 to 50 ppmTi, Zr or Al and more preferably in the range 0.1 to 30 ppm Ti, Zr orAl, based on product ester; and the amount of Ge, Sb or Sn used in adirect esterification or transesterification will be in the range 5 to700 ppm Ge, Sb or Sn, preferably in the range 5 to 400 ppm Ge, Sb or Sn,based on product ester. For polyesterification, the preferred amount ofTi, Zr or Al is in the range 0.2 to 50 ppm Ti, Zr or Al based on productpolyester. The preferred amount of Ge, Sb or Sn used inpolyesterification is in the range 5 to 500 ppm Ge, Sb or Sn.

[0046] Additional compounds may be added to the polyesterificationreaction if required. It is common to add a polymer stabiliser to thereaction mixture to stabilise the polymer against thermal degradation. Acommon stabiliser comprises a phosphorus compound, e.g. phosphoric acid.Colour adjustment compounds may also be added at this stage. Forexample, cobalt compounds, e.g. cobalt acetate, or organic dyes may beadded to further counteract any tendency towards yellowness in the finalpolymer. For textile fibres, dyes, optical brighteners, pigments or dyepretreatments may be added to enhance dye retention or improve thesusceptibility of the polymer to dyeing. It may also be required tocontrol the co-products of the polyesterification process, in particularthe diethylene glycol (DEG) content of the polymer, by addition of DEGsuppressants such as bases or amines, as is known in the art. The DEGcontent of the polymer is believed to affect the thermal properties ofthe polymer. For certain applications, the DEG content should be lowalthough for textile fibre it may be desirable to control the level ofDEG to 0.8-1.5 weight %

[0047] The inventive catalyst combination comprising compound (a) andcompound (b) may be used to make polyester for fiber applicationsincluding textile fiber and industrial fiber; moulding applications,including stretch blow moulding for e.g. rigid packaging such asbottles, jars and clamshell packs, extrusion for e.g. film, includingoriented polyester film, and flexible packaging. The fiber may be madeaccording to known methods cited above.

[0048] The invention is illustrated by the following examples.

EXAMPLE 1

[0049] Preparation of Compound A

[0050] Citric acid monohydrate (132.5 g, 0.63 moles) was dissolved inwater (92.8 g). To the stirred solution was slowly added titaniumisopropoxide (72.0 g, 0.25 moles). This mixture was heated to reflux for1 hour to yield a hazy solution. This solution stripped under vacuum toremove free water and isopropanol. The product was cooled below 70° C.and 32% w/w aqueous sodium hydroxide (94.9 g, 0.76 moles) was addedslowly to the stirred solution. The product was filtered, mixed withethylene glycol (125.5 g, 2.0 moles) and heated under vacuum to removefree water/isopropanol. The product was a slightly hazy, very paleyellow liquid (Ti content 3.85% by weight), which is referred tohereinafter as Compound A

[0051] Preparation of Compound B

[0052] Ethylene glycol (217.85 g, 3.51 moles) was added from a droppingfunnel to stirred titanium isopropoxide (284.8, 1.00 mole) in a 1 literfishbowl flask fitted with stirrer, condenser, and thermometer. The rateof addition was controlled so that the heat of reaction caused thecontents of the flask to warm to about 50° C. The reaction mixture wasstirred for 15 minutes and aqueous 85% wt/wt ammonium lactate (251.98 g,2.00 moles) was added to the reaction flask to yield a clear, paleyellow liquid (Ti content 6.54% by weight).

[0053] Preparation of Compound C

[0054] Following the method for Compound B, ethylene glycol (496.37 g,8.0 moles) was added to titanium isopropoxide (284.8 g, 1.0 mole)followed by reaction with aqueous 60% wt/wt sodium lactate (374.48 g,2.0 moles) to yield a pale yellow liquid (Ti content 4.13% by weight).

[0055] Preparation of Compound D

[0056] To titanium isopropoxide (142.50 g. 0.50 mole) in a one literconical flask, fitted with sidearm condenser, supported on and stirredby means of a magnetic stirrer was slowly added ethylene glycol (248.25g, 4.0 moles) from a dropping funnel. When addition was complete, thecontents were stirred for 15 minutes before adding aqueous 60% wt/wtpotassium lactate (213.03 g, 1.0 mole) by dropping funnel to yield aclear, very pale yellow product (Ti content 3.91% by weight).

[0057] Preparation of Compound E

[0058] Following the method for Compound D, diethylene glycol (127.58 g,1.20 moles) was added to 135.95 g (0.3 mole) zirconium n-propoxide(72.3% wt/wt in n-propanol). To this stirred product was added aqueous60% w/wt sodium lactate (112.04 g, 0.60 mole) to yield a pale yellowproduct (Zr content 7.28% by weight).

EXAMPLE 2

[0059] Preparation of Polymer 1

[0060] Compound A, prepared in Example 1 was used to preparepolyethylene terephthalate (PET) in the following way. Ethylene glycol(930 litres) and terephthalic acid (2250 kg) were charged to a stirredjacketed reactor. The catalyst and other additives were added and thereactor heated to 226-252° C. at a pressure of 2.9 bar to initiate thefirst stage direct esterification (DE) process. On completion of the DEreaction, (i.e. when water production stopped, indicated by a rise incolumn temperature), the contents of the reactor were allowed to reachatmospheric pressure before a vacuum was steadily applied. Sodiumhydroxide (100 ppm) was added as a diethylene glycol suppressant and themixture heated to 294+2° C. under vacuum to remove ethylene glycol andyield polyethylene terephthalate. The final polyester was dischargedonce a constant torque had been reached which indicated an intrinsicviscosity (IV) of around 0.62. The chipped polymer was then subjected tosolid state polymerisation at about 230° C. in flowing nitrogen toincrease the polymer molecular weight so as to have an intrinsicviscosity of about 1.0.

[0061] Polyesters of the invention were made using:

[0062] as catalyst compositions,

[0063] Compound A plus antimony trioxide (at 5 ppm Ti+250 ppm Sb) (i.e.a catalyst composition according to the invention)

[0064] Compound A alone (15 ppm),

[0065] and as comparisons:

[0066] antimony trioxide alone (350 ppm)

[0067] tetra(isopropoxy)titanium (15 ppm) (VERTEC™ TIPT™ available fromICI Synetix).

[0068] Properties of the Polymer Samples.

[0069] Intrinsic Viscosity (IV)

[0070] The polymer intrinsic viscosities were measured by glasscapillary viscometry using 60/40 phenol/1,2,2-tetrachlorethane assolvent at 25° C.

[0071] Thermal Characteristics by DSC Analysis

[0072] Heat-cool differential scanning calorimetry (DSC) experiments on‘re-quenched’ samples were conducted as follows: 10 mg samples weredried at 80° C. in a vacuum oven. These dried samples were then held at290° C. for 2 minutes in a Perkin-Elmer DSC instrument, before beingquenched onto the cold block (−40° C.). The re-quenched samples werethen subjected to a heat/hold 2 minutes/cool procedure, at heating &cooling rates of 20° C./minute on a Perkin-Elmer DSC 7a. The coolingdata quoted below have been corrected by adding 2.8° C. to thecomputer-generated temperatures. The results are shown in Table 1. TABLE1 Metal content IV Tg_(o) Tn_(o) Tn Tp Tc Tc_(o) Catalyst (ppm) (dl/g)(° C.) (° C.) (° C.) (° C.) (° C.) (° C.) Compound 5 + 250 0.95 80.0129.2 149.5 257.1 189.4 201.5 A + Sb2O3 Sb oxide 350 0.99 82.1 132.6155.4 255.9 181.6 194.2 Compound  15 1.03 83.5 na 145.9 258.5 188.3198.4 A TIPT  14 0.99 77 158 180 248 — —

[0073] Rotational Rheometry—Dynamic Oscillation

[0074] The materials were characterised using a Rheometrics rheometer.

[0075] The sample was placed in the rheometer between two 40 mm diameterparallel plates and heated to the measurement temperature 285° C. Thesample was squeezed to remove any voids until a gap of between 1 and 2mm was reached. Any residual material at the edges was removed.

[0076] From the measured torque response an in-phase storage modulus G′,and an out of phase loss modulus G″, have been calculated. A complexviscosity, ETA*, has subsequently been calculated from the moduli.

[0077] For measurements taken in the linear viscoelastic region (strainindependent) it is possible to equate frequency with shear rate andcomplex viscosity with apparent shear viscosity. Therefore for simpleunfilled systems it is acceptable to think of frequency (rads/s) asshear rate (/s) and complex viscosity (Pa.s) as shear viscosity (Pa.s).

[0078] Capillary Rheometry

[0079] The materials were characterised at 285° C. using a Rosandcapillary rheometer. The polymer charge was melted in the heatedrheometer barrel prior to extrusion. The melt was extruded at a range offlow rates through a die 1 mm in diameter and the pressure drop wasmeasured at the die entry at each rate. Two parallel measurements usingdifferent die lengths were made to allow a die entry correction (Bagley)to be made. The apparent shear and elongational viscosity's (Cogswell)were calculated from the die geometry and pressure drops recorded. Unitsof viscosity are Pa.s. Shear rate is a function of the volumetric flowrate and die geometry and is measured in reciprocal seconds (s⁻¹).

[0080] The results in FIG. 4 show that the polymer in which theinventive catalyst of Compound A is present has extensional viscositysignificantly better than that of polymer made with Sb alone. Thisresult is surprising, given that polyesters made using the prior arttitanium catalyst (titanium tetraisopropoxide) had extensionalviscosities significantly reduced from those of polymers made with Sbcatalysts. Polymer molecular weight may be estimated from the zero shearviscosity measurement, which is typically inferred from the complexviscosity at low frequency of oscillation using rotational rheometry.Normally this means that the extensional viscosity correlates with themolecular weight of the polymer, e.g. a polymer with low zero-shearviscosity typically has a low extensional viscosity. FIG. 3 shows thatpolyester made from Sb alone has a higher zero shear viscosity than theinventive combination of Sb and Compound A Based on the prior arttitanium data in FIGS. 1 and 2, one skilled in the art would haveexpected that the inventive catalyst combination would exhibit a lowerextension viscosity. However, transient extensional viscosities (FIG. 4)are essentially identical for polyester made from the Sb control and theinventive catalyst combination. Thus, the present invention haseliminated the large deficiency in reduced extensional viscosity thatoccurred in polyesters made from prior art titanium catalysts.

[0081] We tried using polyester made from titanium tetraisopropoxidecatalyst to make dimensionally stable polyester yarn according to U.S.Pat. No. 5,132,067. With the TIPT polyester, ft appeared possible toachieve higher strength at low dimensional stability or higherdimensional stability at low strength but not both together as waspossible with polyester made from Sb catalyst The differences inTheological characterization discussed above are consistent with, andappear to explain the differences in undrawn response of the twopolyesters. With a significantly lower extensional viscosity, the TIPTpolyester has a relatively lower resistance to being stretched and hencein making industrial fiber from the polyester, more spinline stress,i.e. higher spinning speed, is required in order to produce the sameorientation, e.g., birefringence and crystallinity, in the undrawnindustrial fiber.

[0082] The behaviour of polyester under stretching flow (elongation)would normally be proportional to the molecular weight of the polyester.The catalyst system of the invention, despite the lower molecularweight, demonstrates equivalent or better resistance to stretch flow.This is consistent with the catalyst system of the invention givinghigher spinline stress and ultimately fibre crystallinity.

[0083] Chemical Analysis of Polymers

[0084] The carboxyl end groups were determined by automaticpotentiometric titration whereby the sample is dissolved in a solventmixture of 70% o-cresol/30% chloroform and titrated on an autotitratorwith standardized KOH in methanol The polymers were examined by ¹H NMRspectroscopy to determine the amount of diethylene glycol (DEG) residuespresent in the polymer chain (expressed as weight percent of polymer),the proportion of hydroxyl (OH) end groups present (expressed as numberof end groups per 100 polymer repeating units) and the proportion ofvinyl end groups (VEG) present (expressed as number of end groups per100 polymer repeating units).

EXAMPLE 3

[0085] Preparation of Fibre

[0086] Dried PET chip was fed under nitrogen into a single screwextruder fitted with gear pump, spin block, spin pot and spinnerette.The temperature profile of this system was chosen to give the desiredpolymer melt viscosity. A continuous multi-filament product was producedby passing the molten filaments exiting the spinnerette through a heatedsleeve and quench stack and then drawn between heated godet rolls toproduce a product with the desired draw ratio and total denier. Themulti-filament product was collected on cardboard sleeves using anautomatic doff winder and tested off-line.

[0087] Fibre Properties

[0088] The properties of the fibres made with the three catalyst systemsare shown in Table 2. The fibre made from the TIPT-catalysed polymershowed poor take-up properties and a high rate of fibre breakagecompared with fibres made from the other catalysts. For this reason,detailed measurements were not made.

[0089] The IV loss was measured as the difference between the IV of thechip before extrusion and the IV of freefall fibre. The freefall fibreis fibre allowed to fall freely from the spinneret Carboxyl (COOH)values were also determined on the freefall fibre. The fray count ismeasured by a detector above the take-up winder on fibre spinning. Thisdetector consists of a light-beam which measures loops/broken filamentwithin the fibre. TABLE 2 Compound A + Property Sb₂O₃ Sb₂O₃ Compound AFreefall IV (g/dL) 0.85 0.83 0.88 Extrusion IV Loss 0.10 0.16 0.15 COOH22.5 30.6 20.9 Frays/lb 9.8 49.3

[0090] The density of the undrawn and drawn yarn is a convenient measureof percent crystallinity. Densities of undrawn and drawn yarns weredetermined in n-heptane/carbon tetrachloride density gradient column at23° C. The gradient column was prepared and calibrated according to ASTMD1505-68 with density ranging from 1.30-1.43 g/cm³. Percentagecrystallinity was then calculated from:${{Weight}\quad \% \quad {XTAL}} = {\frac{\left( {{Ys} - {Ya}} \right)\quad \left( {{Yc}/{Ys}} \right)}{\left( {{Yc} - {Ya}} \right)} \times 100}$

[0091] Ys—measured density of sample in gm/cm3

[0092] Ya—theoretical density of 100% amorphous phase (1.335 gm/cm³)

[0093] Yc—theoretical density of 100% crystalline phase (1.455 gm/cm³)

[0094] The crystallinity and orientation index was determined at variousspinning speeds and is shown graphically in FIG. 5. Although quiescentcrystallisation, e.g. by DSC techniques does not always accuratelyreflect spin-line crystallisation kinetics, however as shown in FIG. 5,for a given fibre orientation index, the percent crystallinity is, innearly all cases, higher for polymers containing the mixed catalystsystem of the invention compared to the Sb only polymers. This is inkeeping with the belief that the higher the peak crystallisationtemperature on cooling from melt (Tc) the greater the opportunity fordevelopment of crystallisation in the spinline—all other conditionsbeing constant

[0095] The results show that using the catalyst system andpolyesterification process of the invention it is possible to producepolymer having properties which are comparable with or better thanpolymer made using a standard antimony catalyst, whilst the level ofantimony is considerably reduced. The reduced metal burden of thepolyesters of the invention lead to a cleaner polymer which providesenvironmental benefits and also processing benefits in the end use. Forexample, a high level of antimony catalyst can lead to levels ofinsoluble elemental antimony in the finished polymer which may causebreakage of or defects in a fibre made from such polymer. Reducing theelemental antimony can therefore produce a better fibre and enable thefibre spinning process to be operated at higher speeds and with superior“runnability”. Furthermore, colour management of the polymer, forexample by incorporation of dyes or inorganic toners, may be easierbecause the greying effects of antimony are reduced whilst the polymeris less yellow than a similar polymer containing more titanium.

[0096] The benefits of reduced levels of antimony in the final polymerare useful in most melt processing applications. For example in filmmanufacture the level of imperfections in the film would be expected tobe lower using polyester made according to the method of the invention.The polymer also has a better appearance; the lower levels of antimonygiving a polymer having a better “sparkle”. In bottle manufacture, theimproved melt rheological processing properties may also providebenefits in process stability and product quality. The polyester made bythe process of the invention and using the catalyst of the invention istherefore useful in producing films and rigid pacaking articles such asbottles, trays and clamshell containers.

1. A catalyst composition suitable for use as a catalyst for thepreparation of an ester comprising (a) an organometallic compound whichis the reaction product of an orthoester or condensed orthoester oftitanium, zirconium, or aluminium an alcohol containing at least twohydroxyl groups, a 2-hydroxy carboxylic acid and a base; and (b) atleast one compound of germanium, antimony or tin.
 2. A catalystcomposition as claimed in claim 1, wherein the organometallic compoundis a reaction product of a titanium orthoester.
 3. A catalystcomposition as claimed in claim 1 or claim 2 wherein said alcohol is adihydric alcohol.
 4. A catalyst composition according to claim 3 inwhich the organometallic compound contains from 2 to 12 moles ofdihydric alcohol per mole of titanium or zirconium. 5 A catalystcomposition as claimed in any of claims 1-4, wherein said carboxylicacid is selected from lactic acid, citric acid, malic acid and tartaricacid. 6 A catalyst composition according to claim 1 in which theorganometallic compound contains from 1 to 4 moles of 2-hydroxy acid permole of titanium or zirconium. 7 A catalyst composition as claimed inany of claims 1-6, wherein said base is selected from sodium hydroxide,potassium hydroxide, ammonium hydroxide, sodium carbonate, magnesiumhydroxide, ammonia, tetrabutyl ammonium hydroxide, tetraethylammoniumhydroxide, choline hydroxide, (trimethyl(2-hydroxyethyl)ammoniumhydroxide), benzyltrimethyl ammonium hydroxide, monoethanolamine,diethanolamine, triethanolamine or triisopropanolamine.
 8. A catalystcomposition as claimed in any of the preceding claims wherein theorganometallic compound comprises the reaction product of a titaniumorthoester, citric acid, a dihydric alcohol and an inorganic base inwhich the mole ratio of titanium: acid: dihydric alcohol: base is in therange 1:1.5-3.5:4-10:2-12.
 9. A catalyst composition according to anyone of the preceding claims wherein the compound of germanium isgermanium dioxide or a salt of germanium.
 10. A catalyst compositionaccording to any one of the preceding claims wherein the compound ofantimony is antimony trioxide or a salt of antimony.
 11. A catalystcomposition according to any one of the preceding claims wherein thecompound of tin is a tin salt, a dialkyl tin oxide, a dialkyl tindialkanoate or an alkylstannoic acid.
 12. A catalyst compositionaccording to any one of the preceding claims wherein the weight ratio ofcomponent (a) to component (b) is in the range 1:0-1000, calculated asweight of Ti, Zr or Al to weight of Ge, Sb or Sn.
 13. A process for theproduction of a polyester comprising the reaction of a compound selectedfrom the group consisting of terephthalic acid, dimethyl terephthalate,isophthalic acid, dimethyl isophthalate, dimethyl 2,6 naphthalate ornaphthalene dicarboxylic acid with an alcohol selected from the groupconsisting of 1,2-ethanediol, 1,4-butanediol, 2,3-propanediol,1,6-hexanediol, trimethylol-propane and pentaerythritol in the presenceof a catalyst composition comprising: (a) an organometallic compoundwhich is the reaction product of an orthoester or condensed orthoesterof titanium, zirconium, or aluminium an alcohol containing at least twohydroxyl groups, a 2-hydroxy carboxylic acid and a base, and (b) atleast one compound of germanium, antimony or tin.
 14. A process asclaimed in claim 13 in which the esterification reaction is a directesterification or a transesterification and the catalyst is present inan amount in the range 0.2 to 1200 parts per million calculated as partsby weight of metal with respect to weight of product ester.
 15. Aprocess as claimed in claim 13, wherein the esterification is apolyesterification and the catalyst is present in an amount in the range5 to 500 parts per million calculated as parts by weight of metal withrespect to weight of product polyester.
 16. A process for themanufacture of a polyester article comprising: (i) reacting together acompound selected from the group consisting of terephthalic acid,dimethyl terephthalate, isophthalic acid, dimethyl isophthalate,dimethyl 2,6 naphthalate or naphthalene dicarboxylic acid with analcohol selected from the group consisting of 1,2-ethanediol,1,4-butanediol, 2,3-propanediol, 1,6-hexanediol, trimethylol-propane andpentaerythritol in the presence of a catalyst composition comprising:(a) an organometallic compound which is the reaction product of anorthoester or condensed orthoester of titanium, zirconium; or aluminiuman alcohol containing at least two hydroxyl groups, a 2-hydroxycarboxylic acid and a base, and (b) at least one compound of germanium,antimony or tin (ii) optionally subjecting the resulting polymer to asolid phase polymerisation reaction, to form a polyester material havingan intrinsic viscosity of at least 0.5 dl/g, as measured by the methodof ASTM D-4603, and (iii) forming said polyester article from saidpolymer in the melt phase and (iv) cooling.
 17. The process of claim 16further comprising the additional step of drawing said polyester fibre.18. A polyester article containing residues of a catalyst compositioncomprising: (a) an organometallic compound which is the reaction productof an orthoester or condensed orthoester of titanium, zirconium, oraluminium an alcohol containing at least two hydroxyl groups, a2-hydroxy carboxylic acid and a base, and (b) at least one compound ofgermanium, antimony or tin.
 19. A polyester article as claimed in claim18, which is a fibre, film or container.
 20. A polyester article asclaimed in claim 19 comprising an industrial fibre.
 21. A polyesterarticle as claimed in claim 19 comprising a fibre suitable for use as atextile fibre.
 22. A tire cord comprising said industrial fiber of claim20.
 23. A seat belt comprising said industrial fiber of claim
 20. 24. Arubber reinforced article comprising said tire cord of claim
 22. 25. Atire comprising said rubber reinforced article of claim
 24. 26. A safetyrestraint system comprising said seat belt of claim
 23. 27. A polyesterarticle as claimed in claim 19 comprising a film
 28. A polyester articleas claimed in claim 19 comprising a rigid packaging article including abottle, jar or clamshell package.
 29. A process for the manufacture of apolyester fiber comprising: (i) reacting together a compound selectedfrom the group consisting of terephthalic acid, dimethyl terephthalate,isophthalic acid, dimethyl isophthalate, dimethyl 2,6 naphthalate ornaphthalene dicarboxylic acid with an alcohol selected from the groupconsisting of 1,2-ethanediol, 1,4-butanediol, 2,3-propanediol,1,6-hexanediol, trimethylol-propane and pentaerythritol in the presenceof a catalyst composition comprising: an organometallic compound whichis the reaction product of an orthoester or condensed orthoester oftitanium, zirconium, or aluminium an alcohol containing at least twohydroxyl groups, a 2-hydroxy carboxylic acid and a base, and (ii)optionally subjecting the resulting polymer to a solid phasepolymerisation reaction, to form a polyester material having anintrinsic viscosity of at least 0.5 dl/g, as measured by the method ofASTM D-4603, and (iii) forming said polyester fiber from said polymer inthe melt phase and (iv) cooling.
 30. The process of claim 29 furthercomprising the additional step of drawing said polyester fibre.
 31. Apolyester fiber containing residues of a catalyst compositioncomprising: an organometallic compound which is the reaction product ofan orthoester or condensed orthoester of titanium, zirconium, oraluminium an alcohol containing at least two hydroxyl groups, a2-hydroxy carboxylic acid and a base.
 32. The polyester fiber of claim31 wherein said fiber is industrial fiber. 33 The polyester fiber ofclaim 31 wherein said fiber is a textile fiber 34 A tire cord comprisingsaid industrial fiber of claim
 32. 35 A seat belt comprising saidindustrial fiber of claim
 32. 36. A rubber reinforced article comprisingsaid tire cord of claim
 34. 37. A tire comprising said rubber reinforcedarticle of claim
 36. 38 A safety restraint system comprising said seatbelt of claim
 35. 39 A method of improving extensional viscosity infiber spun from polyester made from titanium catalyst comprising thestep of: using a catalyst composition comprising an organometalliccompound which is the reaction product of an orthoester or condensedorthoester of titanium, zirconium, or aluminium an alcohol containing atleast two hydroxyl groups, a 2-hydroxy carboxylic acid, and a base tomake said polyester. 40 The method of claim 39 wherein said fiber isindustrial fiber. 41 The method of claim 39 wherein said fiber is atextile fiber 42 Fiber having improved extensional viscosity containingresidues of a catalyst composition comprising an organometallic compoundwhich is the reaction product of an orthoester or condensed orthoesterof titanium, zirconium, or aluminium an alcohol containing at least twohydroxyl groups, a 2-hydroxy carboxylic acid, and a base.
 43. The fiberof claim 42 wherein said fiber is industrial fiber. 44 The fiber ofclaim 42 wherein said fiber is a textile fiber